| 1. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 2. |
- Lyon, Keenan, et al.
(författare)
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Parameterization of magnetic vector potentials and fields for efficient multislice calculations of elastic electron scattering
- 2021
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Ingår i: Acta Crystallographica Section A. - : International Union Of Crystallography. - 2053-2733. ; 77, s. 509-518
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Tidskriftsartikel (refereegranskat)abstract
- The multislice method, which simulates the propagation of the incident electron wavefunction through a crystal, is a well established method for analysing the multiple scattering effects that an electron beam may undergo. The inclusion of magnetic effects into this method proves crucial towards simulating enhanced magnetic interaction of vortex beams with magnetic materials, calculating magnetic Bragg spots or searching for magnon signatures, to name a few examples. Inclusion of magnetism poses novel challenges to the efficiency of the multislice method for larger systems, especially regarding the consistent computation of magnetic vector potentials A and magnetic fields B over large supercells. This work presents a tabulation of parameterized magnetic (PM) values for the first three rows of transition metal elements computed from atomic density functional theory (DFT) calculations, allowing for the efficient computation of approximate A and B across large crystals using only structural and magnetic moment size and direction information. Ferromagnetic b.c.c. (body-centred cubic) Fe and tetragonal FePt are chosen to showcase the performance of PM values versus directly obtaining A and B from the unit-cell spin density by DFT. The magnetic fields of b.c.c. Fe are well described by the PM approach while for FePt the PM approach is less accurate due to deformations in the spin density. Calculations of the magnetic signal, namely the change due to A and B of the intensity of diffraction patterns, show that the PM approach for both b.c.c. Fe and FePt is able to describe the effects of magnetism in these systems to a good degree of accuracy.
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| 3. |
- Lyon, Keenan, et al.
(författare)
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Theory of magnon diffuse scattering in scanning transmission electron microscopy
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:21
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Tidskriftsartikel (refereegranskat)abstract
- We present a theory and a simulation of diffuse scattering due to the excitation of magnons in scanning transmission electron microscopy. The calculations indicate that magnons can present atomic contrast when detected by electron energy-loss spectroscopy using atomic-size electron beams. The results presented here indicate that the intensity of the magnon diffuse scattering in bcc iron at 300 K is 4 orders of magnitude weaker than the intensity of thermal diffuse scattering arising from atomic vibrations.
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| 4. |
- Novko, Dino, et al.
(författare)
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Ab initio study of electromagnetic modes in two-dimensional semiconductors : Application to doped phosphorene
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:11
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Tidskriftsartikel (refereegranskat)abstract
- Starting from the rigorous quantum-field-theory formalism, we derive a formula for the screened conductivity designed to study the coupling of light with elementary electron excitations and the ensuing electromagnetic modes in two-dimensional (2D) semiconductors. The latter physical quantity consists of three fully separable parts, namely, intraband, interband, and ladder conductivities, and is calculated beyond the random phase approximation as well as from first principles. By using this methodology, we study the optical absorption spectra in 2D black phosphorous, so-called phosphorene, as a function of the concentration of electrons injected into the conduction band. The mechanisms of phosphorene exciton quenching versus doping are studied in detail. It is demonstrated that already small doping levels (n similar to 10(12) cm(-2)) lead to a radical drop in the exciton binding energy, i.e., from 600 meV to 128 meV. The screened conductivity is applied to study the collective electromagnetic modes in doped phosphorene. It is shown that the phosphorene transversal exciton hybridizes with free photons to form an exciton-polariton. This phenomenon is experimentally observed only for the case of confined electromagnetic microcavity modes. Finally, we demonstrate that the energy and intensity of anisotropic 2D plasmon-polaritons can be tuned by varying the concentration of injected electrons.
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| 5. |
- Snarski-Adamski, Justyn, et al.
(författare)
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Simulations of magnetic Bragg scattering in transmission electron microscopy
- 2023
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 247
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Tidskriftsartikel (refereegranskat)abstract
- We have simulated the magnetic Bragg scattering in transmission electron microscopy in two antiferromagnetic compounds, NiO and LaMnAsO. This weak magnetic phenomenon was experimentally observed in NiO by Loudon (2012). We have computationally reproduced Loudon's experimental data, and for comparison we have performed calculations for the LaMnAsO compound as a more challenging case, containing lower concentration of magnetic elements and strongly scattering heavier non-magnetic elements. We have also described thickness and voltage dependence of the intensity of the antiferromagnetic Bragg spot for both compounds. We have considered lattice vibrations within two computational approaches, one assuming a static lattice with Debye-Waller smeared potentials, and another explicitly considering the atomic vibrations within the quantum excitations of phonons model (thermal diffuse scattering). The structural analysis shows that the antiferromagnetic Bragg spot appears in between (111) and (000) reflections for NiO, while for LaMnAsO the antiferromagnetic Bragg spot appears at the position of the (010) reflection in the diffraction pattern, which corresponds to a forbidden reflection of the crystal structure. Calculations predict that the intensity of the magnetic Bragg spot in NiO is significantly stronger than thermal diffuse scattering at room temperature. For LaMnAsO, the magnetic Bragg spot is weaker than the room-temperature thermal diffuse scattering, but its detection can be facilitated at reduced temperatures.
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| 6. |
- Snarski-Adamski, Justyn, et al.
(författare)
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Simulations of magnetic Bragg scattering in transmission electron microscopy
- 2023
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Ingår i: 2023 IEEE International Magnetic Conference. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- We have modeled the magnetic Bragg scattering in two antiferromagnetic materials, NiO and LaMnAsO, using transmission electron microscopy. Experimentally, Loudon detected these weak magnetic phenomena in NiO. As a more difficult situation with a lower concentration of magnetic elements and higher concentration of heavier non-magnetic elements that significantly scatter, we did computations for the LaMnAsO compound in order to compare our computational replication of Loudon's experimental data. Additionally, we have discussed the antiferromagnetic Bragg spot's thickness and voltage dependency for both compounds. We used two computational methods, one assuming a static lattice with smeared Debye-Waller potentials and the other explicitly taking into account the atomic vibrations within the quantum excitations of phonons model (thermal diffuse scattering). According to the structural study, the antiferromagnetic Bragg spot in NiO is located between the (111) and (000) reflections. However, in LaMnAsO, it is located at the site of the (110) reflection in the diffraction pattern, which is a forbidden reflection of the crystal structure. According to calculations, the magnetic Bragg spot in NiO has an intensity that is much greater than thermal diffuse scattering at room temperature. The magnetic Bragg spot for LaMnAsO is weaker than the thermal diffuse scattering at room temperature, but its identification can be made easier at lower temperatures.
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